Constructing electrical circuits in textile materials presents a number of challenges. Conventional electrical circuits in textiles include conductive fibers knit or woven into a fabric, and capacitance or bioelectric sensors, transducers, or the like inserted into a textile structure. Such efforts have disadvantages, such as conductive fabrics that cannot be worn against a wearer's skin or must be limited to a small surface area. In garments having a sensor added to a fabric, design processes become complicated and manufacturing costs are increased.
An increasingly important field in textiles is that of “intelligent textiles” in which electrical signals representing physiological data are collected from garments and transmitted to remote locations, for example, for monitoring, assessment, and intervention by health care professionals. However, such textile devices are generally not truly “intelligent” textiles, as they comprise solid-state electronics placed in a textile shell and worn as apparel.
Previous efforts have been made to provide such “intelligent textiles.” For example, one attempt includes a deformation-sensitive knitted or woven fabric structure of intertwined yarns having an electrical resistance that varies with degree of deformation. Another attempt to enhance electrical transmissions comprises a sensor array constructed from conductive threads in which the thread contacts are made with piezo-resistive junctions such that contact resistance changes with applied pressure. Another fabric includes a pressure-activated electrical sensor integrated into a knitted fabric such that fiber contact resistance can be related to compression force. Another knitted fabric that is designed to sense pressure and strain utilizes a single conductive yarn type, in which the applied pressure or strain causes different contact areas and resistances between adjacent loops of the yarn. In yet another example, a knitted electronic transducer utilizes a combination of conductive and non-conductive yarns such that extension in the course or wale direction causes loops in the transducer to separate or come together, varying the electrical resistance of the article. However, none of these efforts has addressed the optimal construction of a textile for suitably overcoming the challenges of contact resistance in such a device.
Thus, there is a need for a method for designing a textile structure to control the position and size of yarn contact areas for controlling electrical contact resistance and sensitivity of the structure to deformation. There is a need for such a method that utilizes a predictable stitch structure that improves control of contact resistance. There is a need for such a method that provides a means for varying a textile structure for specific applications. There is a need for such a method that allows use of a single conductive fiber type in a textile sensor. There is a need for such a method that allows the textile structure to be utilized as a sensor for force, pressure, movement or temperature.